extracellular calcium homeostasis Flashcards
calcium and phosphate play a significant role in the formation of what
skeleton and teeth
regulation of biochemical pathways and signalling cascades
what are bones made out of
calcium phosphate
the homeostasis of plasma calcium is achieved by actions on three different hormones what are they
Metabolites of vitamin D
Parathyroid hormone
Calcitonin
what is the function of metabolites of vitamin D
increase calcium uptake
what is the role of the parathyroid hormone (calcium)
hypocalcaemia
acts on bones and increases resorption
What is the role of calcitonin
hypercalcaemia
wants to store calcium, moves Ca from extracellular space to be stored in the bone
where is the parathyroid hormone made
manufactured in chief cells of the parathyroid gland
heterozygous CaSR inactivating mutation in FHH means failure of what
inhibition of PTH secretion in high [Ca2+]e
during hypercalaemia calcium binds to what receptor
and causes what
GQ coupled receptors’
rise in intracellular Ca concentration -> inhibits exocytosis of PTH secretion
what three effects mediate numerous physiological effects
extracellular calcium homeostasis
nutrient sensor - parietal and G cells
enzyme secretion - alpha and beta cells
Where are PTH receptors expressed
osteoblasts in bone
proximal and distal tubules of kidneys
PTH is responsible for increasing
extracellular Ca2+
Bones - 1 degree primary effect
PTH stimulates _______ to recruit osteoblasts
Osteoblasts induce______
cytokines
osteoclasts
GI tract - ddegree - secondary effect
activates synthesis of 1,25-dihydroxyvitamin D and increases transcelllular uptake of Ca2+ from where
small intestine
Kidneys - 1 degree - primary effect
PTH increase ____ reabsorption by increasing activity of __________
Ca2+
Ca2+ channels and pumps
why is a thyroidectomy not fatal
there are small clusters of PTH producing cells outside of the parathyroid gland
trachea
how is vitamin D converted to 1,25-dihyroxyvitamin D
hydroxylations
secondary hydroxylations is regulated by
Growth hormone = ↑
Prolactin = ↑
Oestrogen = ↑
FGF23 = ↓
1, 25-Dihydroxyvitamin D = ↓
what is the primary role of 1,25 dihydroxyvitamin D
contribute to homeostasis of calcium
how does dihydroxyvitamin D contribute to homeostasis in the small intestine
increases calcium absorption
Diffuses into enterocytes and binds to vitamin D receptor (VDR) and increases gene expression
Increases calcium transport across the enterocyte membrane by increased expression of apical Ca2+ channels and basolateral Ca2+ transporters.
how does dihydroxyvitamin D contribute to homeostasis in the kidneys
increases expression of Na+-Pi cotransporter
improves PTH-mediated Ca2+ reabsorption
how does dihydroxyvitamin D contribute to homeostasis in the bone
increases number of osteoclasts
where is calcitonin manufactured
clear cells of the thyroid gland
what does calcitonin respond to
hypercalcaemia
what is an antagonist action of PTH
calcitonin
owhere in the bone are there calcitoonin receptors
osteoclasts
how does calcitonin act on the bone
reduces rate of bone turnover, forcing release of Ca2+ in the bone
testosterone maintains what in calcium homeostasis
bone density
what do glucocorticoids do in calcium homeostasis
decrease maintenance and abundance of osteoblasts
but increase number and function of osteoclasts
Fibroblast growth factor 23 (FGF23) is secreted by what
osteocytes
Fibroblast growth factor 23 (FGF23) production is upregulated when
plasma concentrations rise
Fibroblast growth factor 23 (FGF23) stimulates phosphate loss where
in the urine
what is hypoparathyroidism
lack of PTH
what is hyperparathyroidism
excess of PTH from parathyroid glands
what is the primary cause of hyperparathyroidism
tumors
what is a secondary cause of hyperparathyroidism
chronic kidney disease (lack of 1,25 - dihydroxyvitamin D
calcium malabsorption
